1. Field of Invention
Aspects of this invention are related to surgical systems, and more particularly are related to controlling orientations of a master tool grip and a slave surgical instrument tip in a surgical system when the two are initially misaligned.
2. Related Art
Surgical systems, such as minimally invasive, teleoperated robotic systems, offer patients many benefits, such as reduced trauma to the body, faster recovery, and a shorter hospital stay. Typically, in a surgical system, a surgeon uses a master tool manipulator, sometimes referred to as a master tool, to control movement of a surgical instrument, referred to as a slave surgical instrument.
In one teleoperated surgical system, a master tool grip of the master tool manipulator is specially designed to be both ergonomic and intuitive for controlling the slave surgical instrument. The surgeon holds the master tool grip in a particular way using his/her forefinger and thumb, so that targeting and grasping involves intuitive pointing and pinching motions.
To enable intuitive control of the slave surgical instrument, the master tool grip is ideally aligned in orientation with the slave surgical instrument tip in a view frame of a stereoscopic viewer in the surgical system. The motions of the slave surgical instrument tip ideally follow master tool motions via teleoperation and are consistent in both directions of motion as well as absolute orientation, i.e., the surgical instrument tip motion follows the motion of the master tool grip. If orientation alignment is not achieved between the master tool and the slave surgical instrument tip, the slave surgical instrument tip neither points in the same absolute direction nor rolls along the same axis as the surgeon is pointing with the master tool.
In one aspect, the master tool manipulator uses motors in a gimbal assembly to actively align the orientation axes of the master tool grip in surgeon eye-view coordinates with the associated slave surgical instrument tip in camera view coordinates. This alignment happens automatically before following is engaged between motion of the master tool and motion of the slave surgical instrument.
Specifically, before entering following on the prior teleoperated surgical system, the system tries to align the orientation of the slave surgical instrument tip in a camera frame with the orientation of the master tool grip in an eye-view frame, sometimes referred to as an eye frame. Typically, the teleoperated surgical system performs a master-slave alignment whenever the system transitions from a mode where the orientation alignment between the master tool grip and the slave surgical instrument tip may have been compromised (after a tool change, camera clutch, slave clutch, swapping of arms in a four arm system, etc.).
In the master-slave alignment process, a set of master wrist joint angles are calculated that cause the orientation of the master tool grip in the eye-view frame to match the orientation of the slave surgical instrument tip in the camera view frame, without changing the master tool grip x-y-z position. The master wrist joints are then commanded to match the calculated angles using the motors.
This should result in alignment of the orientations of the master tool grip and the slave surgical instrument tip. However, if a surgeon grasps the master tool grip too firmly while the motors are positioning the wrist joints in the master tool, there may be both displacement and orientation errors between the master tool grip and the slave surgical instrument tip.
After the wrist joints in the master tool grip are commanded to align the orientations of the master tool grip and the slave surgical instrument tip, the teleoperated surgical system again checks that the master and slave orientations match before allowing the user to enter following. If the orientations don't match, a warning message is displayed and the master-slave alignment is attempted again. This process is repeated until the alignment between the orientations of the master tool grip and the slave surgical instrument tip is within an acceptable tolerance, for example, the orientation misalignment between the master and the slave is smaller than ten degrees.
The orientation misalignment is limited to a small angular deviation so that when the master tool is rotated, the slave surgical tip is typically perceived by the surgeon as rolling in the same way. (See FIGS. 4C and 4D and the related discussion below, which demonstrates that when the orientation misalignment is larger than the allowed small angular deviation, the slave surgical instrument tip rotates in an unexpected way when the master tool grip is rotated.)
When the error in the alignment between the orientations of the master tool grip and the slave surgical instrument tip is smaller than the allowed small orientation misalignment, the master tool grip and the slave surgical instrument tip are considered aligned and the teleoperated surgical system enters following. The requirement to have the master tool grip and the slave surgical instrument tip aligned with such a small orientation misalignment often slows down the surgeon's entry into following.